Apparatus and method for controlling power converter

ABSTRACT

A power converter controlling apparatus that can prevent burnout caused by overcurrent and/or overvoltage generated by low power index operation or output short circuit in a high frequency power converter employing a digital controlling method, and a method thereof. The power converter controlling apparatus includes a digital controller which outputs a gate signal for controlling intermittent operation of a predetermined switch based on inputted control data, a detector which generates a detection signal in response to generation of overcurrent and/or overvoltage, and a registration maintenance unit for maintaining a state where the output of the gate signal is shut off, when the detection signal is generated.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/337,592, filed on Jan. 24, 2006, now pending, which in turns claimsthe benefit under 35 U.S.C. §119(a) from Korean Patent Application No.2005-52588 filed Jun. 17, 2005 in the Korean Intellectual PropertyOffice, the entire disclosure of which is hereby incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus and method for controllinga power converter. More particularly, the present invention relates to apower converter controlling apparatus that can prevent burnout caused byovercurrent and/or overvoltage generated by low power index operation oroutput short circuit in a high frequency power converter employing adigital controlling method, and a method thereof.

2. Description of the Related Art

Generally, a power converter such as an inverter uses a semiconductordevice, for example, Metal-Oxide Semiconductor Field Effect Transistor(MOSFET) for power, as a switch, and it controls the amplitude of outputvoltage through the intermittent on/off operation. Herein, an apparatusfor controlling the intermittent operation of the switch, such as apower converter controlling apparatus, can be analog or digital. Ananalog power converter controlling apparatus has an advantage in that itcan perform control at a faster speed. However, since the analog powerconverter controlling apparatus has a fixed circuit, it cannot beequipped with diverse functions, as compared to a digital powerconverter controlling apparatus.

FIG. 1 presents an example of a system employing a power converter. Itshows an image forming apparatus having a Direct Current/AlternatingCurrent (DC/AC) inverter 30 using a digital controlling apparatus. InFIG. 1, an AC/DC rectifier 20 rectifies power source voltage and outputsDC voltage, and the DC/AC inverter 30 receives the DC voltage from theAC/DC rectifier 20, generates high voltage and provides the high voltageto a charged roller 40. Herein, a controlling apparatus 50 controls aduty rate of gate signals which control the intermittent operation of aswitch in order to maintain a phase margin and a real/apparent powerratio at a uniform level based on a resonance frequency by using a PhaseLoop Lock (PLL) method for increased instantaneous power control andpower conversion efficiencies. The DC/AC inverter 30 is equipped with anenvironment checking mode for checking a minimum power transmissionenvironment, when an output end is short. If a minimum powertransmission condition is not fulfilled, the gate signals arepre-scanned at a maximum frequency.

FIG. 2 is a circuit diagram illustrating a conventional power convertercontrolling apparatus. Referring to FIG. 2, the output voltage or outputcurrent measured by diodes D1 to D4, a resistor R1, and a capacitor C1at the output end of a power converter is transmitted to a digitalcontroller 51 through rectification and AC/DC conversion processes. Thedigital controller 51 outputs gate signals for controlling theintermittent operation of a switch based on the transmitted signals.

However, when overcurrent flows through a MOSFET, which is used as aswitch, due to output short circuit and the like, a main switch 53providing the switch or operation power heats up. The generation of heatdegrades the main switch 53 to be burnt out. Time taken for the mainswitch 53 to reach the burnout is in proportion to the quantity ofenergy. In case of a high capacity power converter, the main switch 53can burn out within tens of minutes or seconds.

In the conventional methods, the switch or the main switch 53 isprotected from heat generated from overcurrent and/or overvoltage byusing a thermosensor. However, the protection of the main switch by thethermosensor or a program has a limitation in reliability and increasescosts based on insulation.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide a powerconverter controlling apparatus that can protect a power converteroperating through high-capacity fast switching from overcurrent and/orovervoltage, and a method thereof.

In accordance with an exemplary aspect of the present invention, thereis provided a power converter controlling apparatus comprising a digitalcontroller which outputs a gate signal for controlling intermittentoperation of a predetermined switch based on input control data, adetector which generates a detection signal in response to generation ofovercurrent and/or overvoltage, and a registration maintenance unit formaintaining a state where the output of the gate signal is shut off,when the detection signal is generated. According to an exemplaryimplementation, the power converter controlling apparatus furthercomprises a registration revocation unit for revoking the state wherethe output of the gate signal is shut off according to control of thedigital controller.

The detector can generate the detection signal based on reverse voltagecharacteristics of a control diode. According to an exemplaryimplementation, the power converter controlling apparatus furtherincludes a measurement unit for measuring information for powerinstantaneous control and providing the measured information as thecontrol data.

In accordance with another exemplary aspect of the present invention,there is provided a method for controlling a power converter controllingoutput voltage through intermittent operation of a switch, the methodcomprising outputting a gate signal for controlling intermittentoperation of the switch based on inputted control data, detectinggeneration of overcurrent and/or overvoltage, and maintaining a statewhere the output of the gate signal is shut off, when overcurrent and/orovervoltage is generated. According to an exemplary implementation, themethod further comprises revoking the state where the output of the gatesignal is shut off.

According to another exemplary implementation, the method furthercomprises measuring information corresponding to the output voltage andproviding the measured information as the control data.

BRIEF DESCRIPTION OF THE DRAWINGS

The above aspects and features of the present invention will be moreapparent by describing certain exemplary embodiments of the presentinvention with reference to the accompanying drawings, in which likereference numerals will be understood to refer to like parts, componentsand structures, where:

FIG. 1 is a block diagram showing an example of a system employing apower converter;

FIG. 2 is an exemplary circuit diagram describing a conventional powerconverter controlling apparatus;

FIG. 3 is a circuit diagram illustrating a power converter controllingapparatus in accordance with an exemplary embodiment of the presentinvention; and

FIG. 4 is a circuit diagram describing a power converter controllingapparatus in accordance with another exemplary embodiment of the presentinvention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Certain exemplary embodiments of the present invention will be describedin greater detail with reference to the accompanying drawings.

In the following description, same drawing reference numerals are usedfor the same elements in different drawings, as noted above. The mattersdefined in the description such as a detailed construction and elementsare provided to assist in a comprehensive understanding of theinvention. One of ordinary skill in the art will appreciate that otherimplementations of the present invention can be carried out withoutstrict adherence to the detained description of the examples set forthbelow. Also, well-known functions or constructions are not described indetail for clarity and conciseness.

FIG. 3 is a circuit diagram illustrating a power converter controllingapparatus in accordance with an embodiment of the present invention.Referring to FIG. 3, the power converter controlling apparatus includesa measurement unit 110, a digital controller 120, a detector 130, and aregistration maintenance unit 140.

The measurement unit 110 measures voltage or current from an output endof a power converter for instantaneous power control, rectifies thevoltage or current, performs AC/DC conversion, and outputs a DirectCurrent (DC) voltage value obtained after the AC/DC conversion.

The digital controller 120 utilizes the DC voltage value outputted formthe measurement unit 110 as a control value and generates gate signalsused for on/off switching of a switch. Herein, the amplitude of theoutput voltage is varied according to the duty rate of the gate signals.

The detector 130 includes a Zener diode Z10 and a resistor R11 which areconnected in series, and it detects an overcurrent or overvoltage basedon reverse voltage characteristics of the Zener diode.

The registration maintenance unit 140 includes a silicon controlledrectifier SCR 10, and a resistor R12, and it maintains the detector inthe state where overcurrent or overvoltage is detected and the gatesignals are shut off. In short, since the silicon controlled rectifierSC10 cannot flow current in the turn-off state, diodes G1 to G4 maintainthe off state based on direct voltage connected to one end of theresistor R12, and the gate signal are outputted from the digitalcontroller 120. However, when pulse current generated by overvoltage orovercurrent is inputted into a gate end of the silicon controlledrectifier SCR10 through the Zener diode Z10 or the digital controller120, the silicon controlled rectifier SCR10 is turned on and it can flowforward current from an anode to a cathode. As a result, the diodes G1to G4 are turned on to thereby shut off the output of gate signals.Also, when the silicon controlled rectifier SCR10 is turned on, theturn-on state is maintained although the gate signals inputted into agate end is removed. Therefore, the gate signals are maintained to beshut off.

According to the above-described structure, the gate signals outputtedfrom the digital controller 120 can be automatically shut off in therespect of hardware when overcurrent and/or overvoltage is generated.Therefore, the generation of heat can be prevented in a switch.

FIG. 4 is a circuit diagram describing a power converter controllingapparatus in accordance with another embodiment of the presentinvention. Referring to FIG. 4, the power converter controllingapparatus includes a measurement unit 200, a digital controller 220, adetector 230, a registration maintenance unit 240, and a registrationrevocation unit 250.

The functions and operations of the measurement unit 200, the digitalcontroller 220, the detector 230 and the registration maintenance unit240 are the same as those described with reference to FIG. 3. Thepresent embodiment features the registration revocation unit 250 forperforming revocation while maintaining the shut-off state of gatesignals in the registration maintenance unit 240.

When pulse current caused by overvoltage or overcurrent is applied to agate of a silicon controlled rectifier SCR20 to thereby turn on thesilicon controlled rectifier SCR20, the turn-on state is maintainedalthough the voltage applied to the gate end is removed. In order toturn off the silicon controlled rectifier SCR20, an anode voltage shouldbecome 0 or a minus value. When a revocation signal is supplied from thedigital controller 220 to a base of a transistor Q20, the transistor Q20of the registration revocation unit 250 is turned off and, accordingly,the silicon controlled rectifier SCR20 is turned off. The turn-off ofthe silicon controlled rectifier SCR20 converts diodes G21 and G22 fromthe on state into the off state. Therefore, the gate signals which havebeen shut off can be outputted.

The above two embodiments control the output of two gate signals for thesake of convenience, it is possible to control the output of more gatesignals in the same methods.

As described above, the technology of the present invention can protecta power converter operated through high-capacity fast switching fromerror-causing environments such as overcurrent and overvoltage. Also, itcan shut off output voltage caused by overcurrent and/or overvoltage inthe respect of hardware, it can prevent burnout caused by the generationof heat. Therefore, the present invention can improve reliability in theerror-causing environments and prevent possible exchange of parts.

The foregoing embodiment and advantages are merely exemplary and are notto be construed as limiting the present invention. The present teachingcan be readily applied to other types of apparatuses, and manyalternatives, modifications, and variations will be apparent to thoseskilled in the art. Accordingly, the description of the exemplaryembodiments of the present invention is intended to be illustrative, andnot to limit the scope of the invention which is defined in thefollowing claims and their equivalents.

1. A power converter for an image forming apparatus, comprising: anAC/DC rectifier which rectifies power source voltage and outputs DCvoltage; an DC/AC inverter which is coupled to an output terminal of theAC/DC rectifier, inverts the DC voltage from the AC/DC rectifier to highvoltage, and outputs the high voltage to a load of the image formingapparatus using a switch; and a controlling apparatus which controlsoperation of the switch of the DC/AC inverter; wherein the controllingapparatus comprises: a first circuit unit which is coupled to an outputterminal of the power converter and generates a control signal based onvoltage or current output by the power converter; a digital controllerwhich outputs a gate signal for controlling intermittent operation ofthe switch of the inverter based on the control signal; a second circuitunit which is coupled to the output terminal of the power converter,detects at least one of overcurrent and overvoltage of the outputterminal of the power converter and generates a detection signal basedon detection of at least one of overcurrent and overvoltage; a thirdcircuit unit which receives the detection signal from the second circuitunit, and automatically shuts off an output of the gate signal usinghardware when the detection signal is generated; and a fourth circuitunit which revokes a state where the output of the gate signal is shutoff according a revocation signal of the digital controller.
 2. Thepower converter as recited in claim 1, wherein the second circuit unitis directly connected to the output terminal of the power converter. 3.The power converter as recited in claim 1, wherein the digitalcontroller checks for a presence of at least one of an overcurrentcondition and an overvoltage condition of the power converter based onthe control signal received from the first circuit unit, when thedetection signal is generated by the second circuit unit.
 4. The powerconverter as recited in claim 3, wherein the digital controllergenerates the revocation signal, when the overcurrent condition and theovervoltage condition are no longer present.
 5. The power converter asrecited in claim 4, wherein the digital controller checks an operationstate of the switch, when the overcurrent condition and the overvoltagecondition are no longer present.
 6. The power converter as recited inclaim 1, wherein the second circuit unit comprises: a Zener diode; and aresistor connected in series with the Zener diode; wherein the secondcircuit unit detects at least one of the overcurrent and the overvoltagebased on reverse voltage characteristics of the Zener diode.
 7. Thepower converter controlling apparatus as recited in claim 1, wherein thethird circuit unit comprises: a silicon controlled rectifier to receivethe detection signal, wherein the silicon controlled rectifier is turnedon when the detection signal is received to shut off the output of thegate signal.
 8. A method for controlling a power converter of an imageforming apparatus, the method comprising: generating a control signalbased on voltage or current output by the power converter of the imageforming apparatus; using a digital controller to output a gate signalfor controlling intermittent operation of a switch based on the controlsignal; detecting at least one of overcurrent and overvoltage of anoutput terminal of the power converter and generating a detection signalbased on detection of at least one of overcurrent and overvoltage;automatically shutting off an output of the gate signal using hardwarein response to the generation of the detection signal; and revoking astate where the output of the gate signal is shut off according arevocation signal of the digital controller.
 9. The method as recited inclaim 8, further comprising: using the digital controller to check for apresence of at least one of an overcurrent condition and an overvoltagecondition of the power converter based on the control signal, when thedetection signal is generated.
 10. The method as recited in claim 8,further comprising: using the digital controller to generate therevocation signal when the overcurrent condition and the overvoltagecondition are no longer present.
 11. The method as recited in claim 10,further comprising: using the digital controller to check an operationstate of the switch, when the overcurrent condition and the overvoltagecondition are no longer present.
 12. The method as recited in claim 8,wherein the generating the detection signal comprises: detecting atleast one of the overcurrent and overvoltage based on reverse voltagecharacteristics of the Zener diode.
 13. The method as recited in claim8, wherein shutting off the output of the gate signal is performed byusing a silicon controlled rectifier which receives detection signal.